Figure 2.

(a) Normal stress changes (Δσ_n; bar, fault unclamping positive) produced by the 1944 Tonankai earthquake (finite fault model from Baba et al.³²; see also Fig. S1 and Supporting Information). Seismic source (white box), rectangular sub-faults (white cells) and their surface projection (green lines) are indicated. Small yellow circles indicate mud volcanoes in the Kumano Basin (after Pape et al.⁶; Morita et al.²⁹). The Kumano Basin is almost entirely located above the 1944 fault rupture. Stress changes are resolved on thrust faults (strike = 225°, dip = 40°, rake = 90), which are inferred to control the mud volcano systems in the Kumano Basin. The rupture area of Kato & Ando³¹ for the 1946 Nankaido earthquake (dashed black line) is shown for reference. TF, thrust front; MST, megasplay thrust. (b) Vertical cross section of normal stress changes superposed onto the Nankai subduction margin (simplified from Park et al.³⁰). Both the sedimentary wedge (indicated by gray shading) and the underlying ‘basement’, which collectively indicates dominant igneous and metamorphic rocks (island arc upper crust; Marcaillou et al.⁷⁰), are indicated. Deep-sourced fluids emitted from mud volcano MV#5 are inferred to travel upward along a thrust fault rooted in the subduction interface⁸. A convenient range of stress change values (−5, 5 bar) has been arbitrarily chosen; note that in some models the calculated stresses may exceed this range. In horizontal section a stress is sampled at 7.5 km depth (dashed blue line in b). This figure was generated using the Coulomb 3.4 software (https://earthquake.usgs.gov/research/software/coulomb) and Adobe Illustrator CS3 (https://www.adobe.com).